How do you export GLTF from Blender?
The glTF-Blender-IO addon ships pre-installed when you download Blender 2.80 or higher.  You can find it in the File -&gt; Import and File -&gt; Export menus, and both the *.gltf and *.glb (Binary bundle) forms are supported.
If you can't see those entries in the menus the addon may be installed but disabled in user preferences. To enable it go to Edit &gt; User Preferences Add-Ons, search for GLTF and enable the addon GLTF addon.
If nothing is listed after searching you may have to download and install the addon.
The glTF file format is intended to be a last-mile transmission format.  The data is stored in a manner similar to how a modern GPU expects to find its own graphics memory arranged (with vertex attributes etc), meaning that glTF can be loaded and almost immediately rendered even on mobile devices, in WebGL, without a lot of pre-processing.
The material model in glTF does not support all of Blender's complex shader nodes.  Instead, glTF offers a principled PBR (Physically-Based Rendering) material definition, and the importer/exporter does its best to translate this to/from Blender's Principled BSDF node according to some very specific rules.  The rules for this are laid out in the Blender Manual.

This is the Water Bottle sample model.  This model and other samples can be downloaded from the glTF Sample Models repository.  The glTF-Binary/*.glb form is typically the best version of any given model to download, as it bundles all the model's assets into a single file.